How do I set cell boundries of different sizes within the same coulmn?

 Hi all

I had just helped answer a question about creating a 'header' with line one for a OO Calc spreadsheet. I replied that you just needed to freeze it to make it static. It does bring me to a particular problem I am having however. I have a budget spreadsheet with a line one 'freezed' header. Each cell contains a month of the year. My problem is that I would like to have two side by side cells under each month for projected and actual budget amounts. like this:

M O N T H
---------------------
_______|________
_______|________
_______|________
_______|________

And so on. How do I change the size and number of cells within a coulmn? This would seem counter to the definition of the two untill you see the above and what I am trying to do. The same question goes for rows. Can I make cells A8 and A9 one cell while not affecting the rest of the rows?

I hope I have made my question clear. It's sometimes hard to describe in writing what is easy to see in person.